1. Field of the Invention
The present invention relates to a cam operated switch which is so designed that a switch driven by the cam performs ON-OFF or switchover operations by the rotation of the cam.
2. Description of the Prior Art
As a conventional cam operated switch of this type, one having the structure shown in FIG. 18 is known. In other words, in the cam operated switch shown in FIG. 18, a first contact plate 51 and a second contact plate 52 are disposed on the side of the periphery of a rotatable cam 50. The contact plates 51, 52 have a smaller thickness in the direction of arrows 53, 54, and a greater width in the direction of an arrow 54'. In addition, the second contact plate 52 is formed of an elastic material, and has an urging force in the direction of the arrow 53, a driven member 55 installed at the distal end of the second contact plate 52 being in contact with the peripheral surface of the cam 50. When the cam 50 rotates and causes the driven member 55 to slip down from the high step portion of the cam 50 to a recess 50a, the contact 52a of the second contact plate 52 comes into contact with the contact 51a of the first contact plate 51. When the driven member 55 is raised from the recess 50a to the high step portion, the contact 52a is removed from the contact 51a.
A cam operated switch having the aforementioned contact plates is also known, for example, in the specification of U.S. Pat. No. 3,727,015.
Further, in the construction of the cam operated switch disclosed in the above prior-art patent, three switch blades (corresponding to contact plates 13, 17, 21 of the present application) are each formed by a single plate, and the intermediate portion of each of the switch blades is buried in a terminal block (corresponding to a retainer 11 of the subject application). In addition, in each switch blade, the projection extending from the terminal block to the cam side is moved by the cam in the radial direction of the cam, and the projection extending from the terminal block in the opposite direction serves as a terminal.
In the cam switch having the above-described arrangement, when the second contact plate 52 moves in the direction of the arrow 53 and causes the contact 52a to come into contact with the contact 51a, as described above, there is a possibility that the first contact plate 51 is bent in the direction of the arrow 54 by the pressing force thereof, and the contacting pressure of both contacts 52a, 51a becomes insufficient. When the contacting pressure becomes insufficient, faulty electrical conductance may possibly result between the contact plates 51, 52.
Meanwhile, when the second contact plate 52 moves in the opposite direction and causes the contact 52a to move away from the contact 51a, the first contact plate 51 moves toward the side of the second contact plate 52 due to the springing-back force of the bent first contact plate 51. As a result, the separating distance between the contacts 52a, 51a becomes insufficient. If this separating distance is small, an arc may be established between the contacts 52a, 51a, thereby making an electrical shut-off between the contact plates 51, 52 insufficient.
More specifically, an example of the conventional cam operated switches is disclosed in U.S. Pat. No. 3,752,944, for instance. This cam switch is composed of plural parallel-arranged cams and plural switches corresponding to the number of the cams. Each switch includes a passive blade adjacent to the cam (corresponding to the first contact plate 13 of the present invention) and an active blade remote from the cam (corresponding to the second contact plate 17 of the present invention). These passive and active blades are each formed by a single plate, and each intermediate portion is buried in the wafer (corresponding to the retainer 11 of the present invention). In the active blade, the projection extending from the wafer toward the cam side is moved to and fro toward the passive blade in response to the cam motion, so as to be brought into pressure contact with the passive blade or separated therefrom. In the passive and active blades of each switch, the projection extending from the wafer toward the other side is a plate terminal connectable to a plug-in type connector. A number of plate terminals are all arranged in parallel along the direction of the plate surface. Therefore, the height dimension of the connector connected to these terminals is small.
Further, in the cam operated switch disclosed in the above U.S. patent, a depending spacer is mounted on the passive blade so as to ride on the cam drum in order to eliminate the problem involved in the cam operated switch shown in FIG. 18 of the present application. Therefore, the contact pressure generated when the active blade is in pressure contact with the passive blade is received by the cam drum via the passive blade and the depending spacer, so that a brake force is applied to the cam drum owing to a friction generated between the cam drum and the depending spacer. However, since the passive blade is prevented from being bent in the above-mentioned arrow direction on the basis of the urging force of the active blade, a stable electric conduction can be attained between the active blade and the passive blade.